As a result of the flat panel display widely used in the electrical devices, such as computers, televisions and communication devices, in recent years, the requirements of the flat panel display with high performance have raised. To achieve the purpose of system on panel, the peripheral circuits of the flat panel display have been integrated on the Low Temperature PolySilicon (LTPS) TFT-LCD panel, and using TFTs as the nonvolatile memory is very critical to such purpose.
Currently, most of techniques about integrating the nonvolatile memory on the panel change the structure of a general TFT in order to storage carriers (including electrons and holes). Please refer to U.S. Pub. No. 2004/0206957 “SEMICONDUCTOR DEVICE AND METHOD OF MAINUFACTURE” and U.S. Pat. No. 6,005,270 “SEMICONDUCTOR NONVOLATILE MEMORY DEVICE AND METHOD OF PRODUCTION OF SAME” for related arts regarding using TFT as nonvolatile memory. U.S. Pub. No. 2004/0206957 discloses a plurality of silicon particles for trapping the charge of injected carriers are placed between two gate oxide films; U.S. Pat. No. 6,005,270 discloses a charge storing layer formed between the gate and the gate oxide film.
However, manufacturing processes of the methods for adding the mentioned floating gate or tunneling oxide are more complicated than the general process of TFTs, thus increasing the cost. Moreover, when the electrical components become further miniaturized, the tunneling oxide is formed thinner and prohibits the data retention of the memory. Therefore, there are problems to be solved in the conventional methods for using general thin film transistors as nonvolatile memory.